Catgorising with Euclidean Distance
  - If you have a bunch of items of different categories represented by
    vectors, you can categorise new items by saying the category of
    the known item that is nearest.
 
   - A vector is just a position in a coordinate system.
 
   - In a 2D system, this is just an x and a y coordinate.
 
   - You judge distance using the pythagorean theorem (sqrt(square(x0-x1)+
      square(y0-y1)).
 
   - You can do this in any coordinate system.
 
   - In three dimensions (sqrt(square(x0-x1)+
      square(y0-y1)+square(z0-z1)).
 
   - In 64 dimensions (sqrt(square(x0,0-x0,1)+
      square(x1,0-x1,1)+....square(x63,0-x63,1)).
 
   - How do you do the coursework with this?